Iceland Kinematics From InSAR

Abstract

Time-series of countrywide displacements over Iceland from 2015 to 2021 derived by integrating Sentinel-1 InSAR and GNSS observations • A two-step InSAR tropospheric correction method used to mitigate both short-and long-wavelength tropospheric effects • Results dominated by plate spreading and glacial isostatic adjustment with numerous other smaller-scale signals Abstract Large-scale ground deformation in Iceland is dominated by extensional plateboundary deformation, where the Mid-Atlantic Ridge crosses the island, and by uplift due to glacial isostatic adjustment from thinning and retreat of glaciers. While this deformation is mostly steady over multiple years, it is modulated by smaller-scale transient deformation associated with e.g., earthquakes, volcanic unrest, and geothermal exploitation. Here we combine countrywide Sentinel-1 interferometric synthetic aperture radar (InSAR) data (from six tracks) from 2015 to 2021 with continuous GNSS observations to produce time-series of displacements across Iceland. The InSAR results were improved in a two-step tropospheric mitigation procedure, using (1) global atmospheric models to reduce long-wavelength and topography-correlated tropospheric signals, and (2) modeling of the stochastic properties of the residual troposphere. Our results significantly improve upon earlier country-wide InSAR results, which were based on InSAR stacking, as we use more data, better data weighting, and advanced InSAR corrections to produce time-series of ground displacements instead of just velocities. We fuse the three ascending and three descending track results to estimate maps of East and Up velocities, which clearly show the large-scale extension and GIA deformation. Using a revised plate-spreading and glacial isostatic adjustment models, based on these new ground velocity maps, we remove the large-scale and steady deformation from the InSAR timeseries and analyze the remaining transient deformations. Our results demonstrate the importance of (1) mitigating InSAR tropospheric signals over Iceland and of (2) solving for time-series of deformation, not just velocities, as multiple transient deformation processes are present.

Crustal Characterization of the Hengill Geothermal Fields: Insights From Isotropic and Anisotropic Seismic Noise Imaging Using a 500‐Node Array

“…This consistent accumulation of the subhorizontal formation likely relates to the widespread positive radial anisotropy that we observe at depths >2 km. In fact, such horizontal layering strata are expected throughout the Hengill area, suggesting the negative anisotropy we observe in the top 2 km of the crust likely reflects the effects of the rift and fissure extension in this area (Cao et al, 2023;Drouin & Sigmundsson, 2019), which generates an excess development of vertical fractures and cracks within the shallow layered crust. This allows seismic waves to travel faster in the vertical direction despite the horizontal layering.…”